The blue whirl flame
Sriram Hariharan (University of Maryland)
We may be one step closer to solving the mystery of the blue whirl flame – a soot-free flame that consumes all the fuel it encounters.
The elusive phenomenon was first discovered several years ago by researchers who were investigating more efficient ways of using fire to clean up oil spills in the ocean. They were experimenting with fire whirls – whirlwinds naturally induced by fire – and accidentally generated a clean, whirling blue flame.
Since then, researchers have been trying to determine the structure of this mysterious blue whirl flame, with the hope of harnessing it for cleaner and more efficient combustion.
Joseph Chung and Xiao Zhang at the University of Maryland, College Park, and their colleagues created a computer simulation of the experimental conditions that generated the original blue whirl flame. By gradually adjusting different parameters, such as the ratio of fuel to air, and comparing it with video footage of the blue whirl, the team was eventually able to simulate the flame and analyse its structure.
They discovered that the blue whirl is actually the result of three different types of flame merging. These include an invisible outer flame, where there is more oxygen than fuel, and two visible inner flames, where the ratio of fuel to oxygen is higher.
Knowing the constituent flame types that make up the blue whirl’s structure could enable it to be recreated under more controlled conditions without the need to go through the fire whirl stage, which is dangerous and difficult to contain, says Chung.
It could also help guide the design of equipment to harness the blue whirl flame for cleaner and more efficient combustion. “Burning hydrocarbons is one of the main sources of our energy and unfortunately this has a serious impact on the environment,” says Zhang. “The blue whirl itself shows a possible way of burning that could greatly reduce this pollution and so we are very motivated to explore this potential for cleaner combustion.”
Today, there is a clear emphasis on improving sustainable energy technology, says Wilfried Coenen at the University Carlos III of Madrid, Spain, but there are still benefits to be gained from finding ways to reduce emissions from burning hydrocarbons.
“Soot production in the blue whirl is much, much lower than in a regular, yellow flame,” he says. “There is certainly interest in exploring the possibility to mimic the flow field and combustion process of the blue whirl in already existing applications, to reduce emissions.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.aba0827
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